1. Field of the Invention
The present invention relates to a liquid crystal display device including an optical sensor, and a black matrix substrate and a color filter substrate provided in the liquid crystal device.
2. Description of the Related Art
An active-matrix liquid crystal display device drives a liquid crystal using thin-film transistors, for example, amorphous silicon TFTs (Thin Film Transistors) or polysilicon TFTs. The liquid crystal display device is used in various devices including a mobile device such as a cellular phone, and a large-sized television.
The liquid crystal display device cannot emit light itself and can be classified into a reflective type and a transmissive type. The reflective liquid crystal display device provides display by allowing external light such as natural light to enter a liquid crystal screen so that the light passes through a liquid crystal layer and is then reflected. The transmissive liquid crystal display device includes a light source located on a surface lying opposite an observer, to provide display using transmitted light from the light source. Furthermore, a transflective liquid crystal display device has been put to practical use; the transflective liquid crystal display device operates as a transmissive type using a light source or a reflective type utilizing sunlight or room light depending on an external-light environment (bright or dark environment).
In the liquid crystal display device provided in a mobile device such as a cellular phone or a portable small-sized personal computer, inputting via a keyboard is difficult. Thus, for example, a capacitance-type touch panel or an electric resistance-type touch panel is often installed on a front surface of the liquid crystal display device. However, the touch panel installed on the liquid crystal display device increases the thickness of the liquid crystal display device. In particular, in the liquid crystal display device in the mobile device, light loss attributed to the touch panel may occur, such as surface reflection or loss of transmitted light. This may degrade the quality of liquid crystal display images.
In recent years, the brightness of the transmissive liquid crystal display device has been significantly increased by the increased luminance of a fluorescent lamp installed on a rear surface of the liquid crystal display device or the use of a LED power source with a high luminance. However, when a viewer watches television with such the transmissive liquid crystal display device at night or in a dark place, the screen may be too bright and difficult to see. Furthermore, in the transmissive liquid crystal display device, the light source on the rear surface accounts for about 80% of power consumption. Thus, a reduction in power consumption has been a major challenge.
Furthermore, in recent years, there has been a demand to ensure security for an operation of the liquid crystal screen not only for a device in company and a device such as an automated teller machine in a financial institution but also for the liquid crystal display device in the mobile device.
A Document 1 (Jpn. Pat. Appln. KOKAI Publication No. 2007-47789) discloses a technique that uses an optical sensor. The optical sensor is formed on a TFT substrate on which a thin-film transistor driving a liquid crystal is formed, and is utilized to adjust the brightness of the liquid crystal display device.
A Document 2 (Jpn. Pat. Appln. KOKAI Publication No. 2005-352490) discloses a technique that also uses an optical sensor. The optical sensor is formed on a TFT substrate on which a thin-film transistor driving a liquid crystal is formed, and is used as a touch panel.
A Document 3 (Jpn. Pat. Appln. KOKAI Publication No. 2008-89619) discloses a technique that also uses an optical sensor. The optical sensor is located around the periphery of a TFT substrate on which a thin-film transistor driving a liquid crystal is formed. A blue, green, or red color filter is formed above the optical sensor and used depending on the type of external light.
A document 4 (Jpn. Pat. Appln. KOKAI Publication No. 2009-129397) discloses a display device comprising a plurality of color filters for the respective colors and a photoelectric sensor provided behind a detection filter in which at least two color filters are stacked. The document 4 subtracts a detection value of a separately formed noise removal sensor, from a detection value of the photoelectric sensor.
A document 5 (Jpn. Pat. Appln. KOKAI Publication No. 2009-128686) discloses a display device comprising a first optical sensor section and a second optical sensor section in which two types of color filters are stacked.
The document 1 does not disclose luminance adjustment used for the type of external light { sunlight on a sunny day, sunlight on a cloudy day, or light from a fluorescent lamp) or human visibility.
In the document 2, an error in a user's touch with a liquid crystal screen may result from the influence of the intensity of external light or backlight luminance. Furthermore, the document 2 describes an arrangement of a first optical sensor and a second optical sensor but fails to take into account significant individual differences in fingers among users and the need for authentication for security.
The document 3 fails to take into account the influence of wavelength distribution of light from a backlight, a variation in the temperature of dark current in the optical sensor itself, and variations among elements. It is hoped that the types of external light are distinguished in high accuracy rather than the document 3 is applied. Moreover, the document is a luminance adjustment technique based on external light, and fails to take touch panel inputs with the finger or the like into account.
The document 4 is different from a technique for optical wavelength separation in a visible range carried out by the photoelectric sensor because transmittance is high in the wavelength range of invisible light as described in Claim 2 of the document 4. Thus, the document 4 is not a technique for determining the type of external light and ensuring security or a technique used to adjust the luminance of the liquid crystal display device. Hence, the document 4 is not a technique for distinguishing visible light from the other types of light. Furthermore, the document fails to describe a spectral characteristic of a light shield section provided in a noise removal sensor according to Claim 7 of the document 4 and the sensitivity of a sensor in the wavelength range of invisible light, and fails to clearly specify a detection value from the noise removal sensor associated with a subtraction process, and the result of the subtraction process.
The document 5 proposes a technique to process the difference between a detection signal from a first optical sensor and a detection signal from a second optical sensor section in which the two types of color filters are stacked, as disclosed in claim 1 of the document 5. However, the sensor disclosed in the document 5 has difficulty accurately separating external light into blue (B), green (G), and red (R) and thus accurately determining the type of the external light. Similarly, the technique of the document 5 has difficulty accurately distinguishing a skin color including red and green, from the other colors, and cannot be appropriately used to determine a finger input. Moreover, the detection signal involves an error in transmitted light corresponding to a red range or a near-infrared range (for example, between 700 nm and 800 nm) as shown in FIGS. 6 and 8 of the document 5. Separating a color from one another accurately is difficult. The difficulty in color separation will be described below. As shown by a green absorptivity in FIG. 6 of the document 5, green light has a transmission range between about 700 nm and about 800 nm. Furthermore, as shown in FIGS. 8 and 9 of the document 5, a wavelength corresponding to the 50% transmittance of the optical transmission range of the infrared filter is determined to be about 780 nm. In the technique disclosed in the document 5, the detection signal contains a red optical component and involves an error in a range between 700 nm and 800 nm outside the visible range. Moreover, the document 5 discloses no color materials used for red (R) and blue (B), and fails to describe a specific technique for constructing the red (R) and blue (B) color filter and the infrared filter.